Acoustical methods have been widely used for almost 30 years for flaw detection, visualization, and local parameter measurement of different materials. Acoustical techniques are irreplaceable tools for nondestructive evaluation of adhesive-bonded composites and components for the electronics, aeronautics, and automotive industries in the high-technology sector. In the last decade, much progress has been made in the development and improvement of acoustical methods for the investigation of adhesively-bonded structures. These methods allow us to detect voids, delaminations, porosities, cracks, and poor adhesion. In this paper, the most common techniques, such as normal and oblique ultrasonic scans, resonant ultrasonic spectroscopy, and Lamb-wave methods are reviewed. Analysis of the typical defects that can occur in adhesive joints and their causes are presented. The progress of the study of the adhesion mechanism and the role of the interfacial properties and surface conditions in the adhesion process is surveyed. PACS No.: 81.70.Cv

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